# std::ranges::in_found_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
template< class I > struct in_found_result; |  | (since C++20)

`ranges::in_found_result` is a class template that provides a way to store an iterator and a boolean flag as a single unit.

This class template has no base classes or declared members other than those shown below. Thus it is suitable for use with structured bindings.

All special member functions of this class template are implicitly declared, which makes specializations be aggregate classes, and propagate triviality, potentially-throwing-ness, and constexpr-ness of corresponding operations on data members.

### Template parameters

I | - | the type of the iterator that the `ranges::in_found_result` stores.

### Data members

Member name | Definition
in | a value (that is supposed to be an iterator) of type `I`. It is declared with `[[no_unique_address]]` attribute. (public member object)
found | a boolean flag (that may show whether an appropriate range can be found) of type bool. (public member object)

### Member functions

## std::ranges::in_found_result::operator in_found_result<I2>

template<class I2> requires std::convertible_to<const I&, I2> constexpr operator in_found_result<I2>() const &; | (1) |
template<class I2> requires std::convertible_to<I, I2> constexpr operator in_found_result<I2>() &&; | (2) |

Converts *this to the result by constructing every data member of the result from the corresponding member of *this.

1) Equivalent to return {in, found};.
2) Equivalent to return {std::move(in), found};.

### Standard library

The following standard library functions use `ranges::in_found_result` as the return type:

##### Algorithm functions
ranges::next_permutation (C++20) | generates the next greater lexicographic permutation of a range of elements (algorithm function object)
ranges::prev_permutation (C++20) | generates the next smaller lexicographic permutation of a range of elements (algorithm function object)

### Synopsis

    namespace std::ranges
    {
        template<class I>
        struct in_found_result
        {
            [[no_unique_address]] I in;
            bool found;

            template<class I2>
            requires std::convertible_to<const I&, I2>
            constexpr operator in_found_result<I2>() const &
            {
                return {in, found};
            }

            template<class I2>
            requires std::convertible_to<I, I2>
            constexpr operator in_found_result<I2>() &&
            {
                return {std::move(in), found};
            }
        };
    }

### Notes

Each standard library algorithm that uses this family of return types declares a new alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.

The names for such aliases are formed by adding the suffix "`_result`" to the algorithm's name. So, the return type of `std::ranges::merge` can be named as `std::ranges::merge_result`.

Unlike std::pair and std::tuple, this class template has data members of meaningful names.

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <iterator>
    #include <ranges>

    int main()
    {
        int v[] {1, 2, 3};

        const auto result = std::ranges::next_permutation(v);

        std::ranges::for_each(std::cbegin(v), result.in, [](int e) {std::cout << e << ' ';});

        std::cout << std::boolalpha << "\n" "result.found: " << result.found << '\n';
    }

Output:

    1 3 2
    result.found = true

### See also

pair | implements binary tuple, i.e. a pair of values (class template)
tuple (C++11) | implements fixed size container, which holds elements of possibly different types (class template)

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